(1) Field of the Invention
THIS INVENTION relates to a method of, and apparatus for, computerised colour matching.
(2) Prior Art
Colour matching is a major problem in many industries, including automobile repair; paint and dye manufacture; printing; and fabric dyeing.
Tooth colour matching is a major problem for dentists and dental technicians when preparing dental caps, crowns or bridge work. They must seek to match the cap, or teeth on the bridge, to the surrounding natural teeth. At present the method is subjective and the results very much dependent on the skills of the person doing the colour matching.
The dental technician is supplied with a "colour map" of the tooth by the prescribing dentist or the map may be drawn by the dental technician, the map being made by comparison with standard porcelain chips. From that "colour map", the technician must build the dental caps/or prosthetic teeth being aware of the following problems:
(a) the dentist and the technician are most likely to have different colour perceptions of the colours under a standard reference light, let alone under different lights;
(b) there are variations in the colour of the porcelain powders as supplied by the various manufacturers against standard "shades" (or coded colours);
(c) some of the standard shades are very similar and therefore difficult to separate by eye;
(d) the depth of the dentine layer (or its translucency) affects the final colour; and
(e) the moisture content of the porcelain mix, the mix density, the firing frequency and temperature and the permeation of oxides through the opaque layer all affect the final colour.
Because of all these problems, colour mismatches may occur 10+% of the time.
In an effort to reduce the problem, a colour mixture indicator device as disclosed in U.S. Pat. No. 4,657,399 (Neil R. Hall) was developed where colour samples were provided in an array where the selected colour is either one of the samples or a mixture of the colour of two adjacent samples.
While this indicator is an improvement over the conventional porcelain colour chips, colour mismatches still occur.